The revolt of the once outwardly docile Christian Lebanese Forces militia has embarrassed President Hafez Assad of Syria just as he was savoring the spectacle of his Israeli adversaries' messy, unconditional withdrawal from Lebanon.

Assad is faced with two unpalatable choices. If he cracks down militarily against the rebels, he risks fracturing Lebanon's fragile Pax Syriana. If he does nothing, he risks the humiliation of the Syrian-sponsored "national unity" government in Beirut under the rebels' former commander in chief, President Amin Gemayel.

In the 10-year-old Lebanese conflict, Syria has used its superior firepower twice to batter the Lebanese Forces -- first in Beirut in 1978, then in the Christian mountain city of Zahleh in 1981.

But using Syrian force now would risk ruining Assad's carefully nurtured image of a benevolent Syria determined to reconcile the warring Lebanese factions in the "national unity" government stitched together last spring.

The now year-old Pax Syriana, which replaced discredited American and Israeli influence, turns on Assad's control of all Lebanese factions, carefully balancing them off to prevent outright winners, losers or, especially, challengers to his authority.

Whatever deep-seated differences separate the Druze and the Shiite Moslems from both Gemayel and the Lebanese Forces, attacking the Christian heartland is dangerous.

The Syrians did not station troops permanently in the heartland -- but did elsewhere -- in the heyday of their alliance with the Lebanese Forces in 1976 and 1977. They reportedly are loath to pay the political and military price of doing so now.

A possibly apocryphal story making the rounds well before this week's revolt had Gemayel pleading with Syrian Vice President Abdul Halim Khaddam to use Syrian troops to remove the Lebanese Forces' "customs post" at Barbara at the northern end of the Christian enclave.

Gemayel was said to have explained that despite his nominal control of the Lebanese Forces, in fact he could not dislodge Samir Geagea, the keeper of the "customs post" who emerged as the revolt's leader this week.

"No," Khaddam was said to have replied, "Syria does not want to spill more Christian blood." If that still reflects official Syrian thinking -- or if it ever did -- there would appear to be little Assad can do but back off, at least for the time being.

Some analysts believe that if Assad does strike he may call upon former president Suleiman Franjieh, a rival Maronite Christian leader who never has forgiven the Gemayel family or Geagea for the 1978 assassination of his son, Tony.

But the political price of doing nothing would be high, especially in the Middle East, where major players fear that any show of weakness can be interpreted as a fatal blow to their aura of power.

The rebels have cleverly boxed Assad in. Despite Lebanese government denials, Lebanese Forces spokesmen have insisted that Assad wanted Gemayel to accept a purported 10-point package that in essence would have made Lebanon little more than a formal appendage of Syria.

Seen in this light, the Lebanese Forces' revolt is aimed less at removing Gemayel from the presidency, traditionally reserved for fellow Maronites, than at stiffening the president's backbone and forcing him to resist Syrian demands.

Even so, Gemayel is unlikely to emerge with his already much battered prestige intact.

Following the death last year of Pierre Gemayel, his father and founder of the Phalangist Party in 1936, the president moved to consolidate formal control over the party and the Lebanese Forces, which was established by his late brother Bashir as his own personal power base.

Distrusted by the Druze and the Moslems who had welcomed his election in 1982, Amin Gemayel on paper had overcome the initial misgivings of his own Maronite community still grieving over Bashir Gemayel's assassination.

Yet replacing one relative with another as Lebanese Forces commander and excommunicating Geagea proved illusory victories.

Geagea's revolt, in fact, reflected a deliberate effort to end the Gemayel family's control of the Phalangist Party and the Lebanese Forces. It was his hatred of feudal family domination in the north that prompted his widely reported role in the killing of Tony Franjieh and he was in open conflict with Bashir Gemayel in the months before the Lebanese Forces' founder was assassinated in 1982.

Recently, Geagea resisted President Gemayel's demands that the Lebanese Forces open up the coastal highway north of Beirut as part of a much-delayed effort to stitch the warring baronies back into a single entity under Syrian tutelage.

Although Christian civilians increasingly question their zeal, the Lebanese Forces feel strongest when the heartland is threatened -- by Palestinians, Syrians or pro-Iranian Shiite Moslem fundamentalists bent on establishing an Islamic republic.

The rebels run the gamut of Lebanese Forces factions, uniting former pro-Israeli commanders with once pro-Syrian officials. Significantly, their manifesto was proclaimed at the home of Bashir Gemayel's widow, Solange, who has never hidden her contempt for her brother-in-law.

Given the mutual backbiting between Jerusalem and the Lebanese Forces over the failure of Israel's 1982 invasion, the Israeli role in the revolt is thought to be essentially secondary. Nonetheless, rumors of arms shipments to the rebels circulate, as do tales of Israeli pleasure in creating problems for Syria.